The present invention relates to navigation systems and more particularly, the present invention relates to a database construction that facilitates the delivery of geographic information to navigation system units from a remotely located geographic database.
Navigation systems provide various useful features, such as calculating routes to desired destinations, providing guidance for following calculated routes, displaying maps, and so on. In order to provide these various kinds of useful features, a navigation system uses geographic data. There are various computer architectures for navigation systems that use geographic data to deliver navigation-related and map-related features. In one type of architecture for a navigation system, end users (such as vehicle drivers) have navigation system units in their vehicles. These end users' navigation system units obtain data from a remotely located geographic database. The remotely located geographic database contains a relatively large amount of geographic data. A server associated with the remotely located geographic database handles requests for navigation-related or map-related services from end users' navigation system units. When an end user's navigation system unit requests data, the server accesses the remotely located geographic database associated therewith to obtain the necessary data to respond to the request and then sends the data to the requesting end user's navigation system unit.
This type of navigation system architecture provides several advantages. One advantage relates to providing updated geographic data. There is a continuing need to update the geographic data used by a navigation system. For example, new streets are built, road construction closes roads, detours are established, new businesses open, posted speed limits change, new turn restrictions are established at intersections, streets are renamed, and so on. These kinds of changes can affect travel through a geographic area. Accordingly, the geographic data used by a navigation system should be updated on a regular basis in order to accurately reflect changes in the represented geographic features. A computer architecture in which individual navigation system units obtain geographic data from a single central geographic database affords an advantage with respect to the updating of the geographic data. With a computer architecture in which individual navigation system units obtain data from a single geographic database associated with a central server, updates need to be applied only to the central database.
A consideration to be addressed in a navigation system in which data are transmitted from a central geographic database to end users' navigation system units relates to the selection of data to be transmitted. If large amounts of data are sent to an end user's navigation system unit, the unit may require significant memory or data storage resources in order to handle the large amounts of data. Also, if large amounts of data are sent to each end user's navigation system unit, the communications system used to carry these data has to have a corresponding large capacity. On the other hand, if the end user's navigation system unit does not receive sufficient data or appropriate data, the end user's navigation system unit may not be able to provide the desired function, such as the displaying a map of the roads around the end user's position. Accordingly, in a navigation system in which data are transmitted from a central geographic database to end users' navigation system units, there is a need to send all the data that may be needed on an end user's system but not to send data that would not be needed.